Rubber curing systems



United States Patent ()fiice 3,375,234 Patented Mar. 26, 1968 3,375,234RUBBER CURING SYSTEMS Samuel Gelfand, Niagara Falls, N.Y., assignor toHooker Chemical Corporation, Niagara Falls, N.Y., a corporation of NewYork No Drawing. Filed Feb. 26, 1964, Ser. No. 347,359

17 Claims. (Cl. 260-795) This invention relates to improvements in thevulcanization of elastomeric polymers and copolymers by sulfur and apolyhaloaliphatic compound.

The vulcanization of highly unsaturated elastomers such as naturalrubber with sulfur and certain moderating accelerators, such asderivatives of guanidine and thiazole, is known. Also known is thevulcanization of rubber having low unsaturation by using sulfur, zincoxide and an accelerator, such as thiuram derivatives anddithiocarbamates. These systems are not effective for saturated polymerssince no useful vulcanizates are formed. Also known is the vulcanizationof saturated polymers by peroxides such as dicumyl peroxide, alone or incombination with sulfur. Recently, octachloropropane andoctachlorocyclopentene, in combination with sulfur, have been found tobe useful vulcanizing agents for saturated polymers. However, thevulcanizates formed by vulcanizing saturated polymers with these curingsystems are deficient in certain properties as compared to peroxidevulcanizates. Among the deficiencies noted is the much lower state ofcure, i.e., vulcanization.

It is an object of this invention to obtain improved chlorocarbon cures.Also an object is to obtain vulcanizates with higher states of cure.

A further object is to obtain vulcanizates with tensile properties andstate of cure comparable to such properties of those cured withperoxides. Further objects will be apparent from the followingdiscussion.

Now there has been found a polyhaloaliphatic compound which incombination with sulfur is satisfactory for the vulcanization ofsaturated polymers so that the resulting vulcanizate has a state of curecomparable to that obtained when a peroxide curative is employed (givesa significantly improved state of cure as compared to known chlorocarboncures). The vulcanizates of this invention have a high degree of crosslinking as evidenced by good low temperature flexibility, absence ofmold staining, permit higher loadings with pigment without loss ofphysical properties and high modulus.

Modulus is defined by Americal Society for Testing MaterialsSpecification D 412-51T as the amount of pull in pounds per square inchrequired to stretch the test piece of a given elongation.

In accordance with this invention, there is provided a composition whichcan be vulcanized comprising decachlorobutane in combination with sulfurand an elastomeric composition. Preferably from 0.1 to 3 parts ofdecachlorobutane (C Cl are mixed with sulfur and 100 parts elastomer,while better products are obtained .when the decachlorobutane isemployed in an amount from 0.5 to parts. Suitably, the amount of sulfurwill be between 0.1 and 10.0 parts and preferably from 0.5 to

5.0 parts. The resulting mixture is then cured by heating to avulcanized product. To further improve the process, zinc oxide, andmetallic accelerators, such as ferric chloride, in various amounts, canbe added to the mixture.

The elastomers suitable for use in this invention includepolyisobutylene and the nearly amorphous polymers and copolymers ofalpha olefins, such as polyethylene and polypropylene,ethylene-propylene copolymers (EPR), ethylene-propylene-minor amountnonconjugated diene terpolymer (EPT) and polymers and copolymers derivedfrom other alpha olefins containing three to five carbon atoms, such asbutene-l and pentene-l. Additionally, polyisobutylene, polybutadiene,ethylene propylene terpolymers and unsaturated ether polymers aresuitable for use with this invention. Polyethylene, polypropylene andEPR polymers are very desirable for use in this invention. The alphaolefin polymers may be produced with organo-metallic catalysts andsupported metal oxide catalysts, as described in great detail in thetext Linear and Stereoregular Addition Polymers; Polymerization withControlled Propagation, Gaylord, N. G. and Mark, H. F., IntersciencePublishers, New York, 1959. Monomers of the type disclosed hereinbeforeare readily polymerized to solid polymers. The reaction is carried outin the presence of an inert hydrocarbon diluent, suitably purified ofcatalyst poisons, at a temperature in the range of 50 to 230 degreescentigrade. At the conclusion of the reaction, the polymer can beremoved from the resulting solution or suspension by evaporation of thediluent, whereupon the polymer is treated for removal of catalystresidues.

The elastomeric composition may be prepared by using conventionalcompounding and mixing equipment of the rubber manufacturing industry.Ingredients and processing procedures are described in the VanderbiltRubber Handbook (6th edition), R. T. Vanderbit, New York, 1958.

When the elastomeric composition is mixed on a mill, the polymer isbanded on the slow roll and decachlorobutane and sulfur are added.(hitting and blending the cuts three-fourths of the way across the rollgives uniform mixing. However, the batch should not be cut when drypigments are present in the rolling bank. Half of the filling pigment isthen added, cut and blended into the batch, and then the procedure isrepeated for the second half. Softeners, Waxes, and accelerators may beadded in that order. The batch is then cut, blended and refined until itis a uniform composition, Time .to complete the mixing is based on thetime taken to blend in all of these ingredients properly, and yet notinitiate cross linking of the composition. A typical mixing temperaturerange for mill mixing of elastomeric compositions is from about 5 0 todegrees centigrade, while temperatures employed by internal mixers mayexceed degrees 'centigrade.

In addition, one can also obtain improved results by subjecting thepolymer and the decachlorobutane of the invention to an operation calledmaster batching prior to incorporation of the other ingredients. Thecompositions of this invention were prepared using the abovedescribedmethods.

It is often advantageous to add pigments, oils and other compoundingingredients to the elastomeric composition in order that the most usefulproperties for a particular application be obtained. The fillers whichcan be used 4 include various carbon blacks, clay (both hard and soft),failure occurred, as indicated by the appearance of cracks silicas, andwhitings. The best results are obtained when in the rubber. CompositionA failed after 14 flexes, Wherethe semi-reinforcing and high reinforcingfurnace and as Composition B failed after only 7 flexes. The flex lifechannel blacks, commonly known as super abrasi n furof Composition A iscomparable with similar compositions nace (SAP), easy processing channel(EPC), semicured with dicumyl peroxide. reinforcing furnace (SRF), highabrasion furnace (HAP), A hot master batch of all ingredients common toComand medium processing channel (MPC) are used. The positions C and Dwas prepared on a large mill. The caramount of filler used generallyranges up to 200 parts by bon filled polymer was heated at 105 to 110degrees cenweight, with the preferred amount being from 20 to 75 tigradeuntil the weight was constant. The curing inparts per 100 parts ofelastomer. 10 gredients were then mixed on a hot mill. Thereafter, theIt is also advantageous to incorporate into the clastoremainingingredients of Compositions C and D were meric composition metallicaccelerators, which include added to portions of the hot master batch.This hot milling the metals, inorganic metallic compounds and themetallic gave better tensile properties than Compositions H, I salts ofcarboxylic acids. Suitable accelerators are metal and I which wereprepared in an identical way on a cold halides, as well as the oxidesand carbonates, and the mill. The samples were cured in a thread moldand metallic salts of alkyl monoand dicarboxylic acids. tested fortensile properties in a Model I P2 Scott Tensile Preferably, theseaccelerators include ferrous oxide, ferric Tester. Typical thread samplecross-sections Were 0.025 oxide, iron chlorides, zinc chloride, aluminumchloride, inch by 0.030 inch. When compared against Compositionl iron2-ethylhexoate, iron tallate, zinc stearate and iron D, Composition Cshows substantially higher modulus distearate. A suitable amount ofthese accelerators is from 29 values at 200 and 300 percent elongattion.Tensile prop 0.1 to 10 parts, preferably 0.5 to 7 parts. erties ofCompositions C and D were also obtained when After making the mixturesof described components by the compositions were cured at 145 degreescentigrade a process such as that described, the elastomeric comfor 40minutes and at 160 degrees centigrade for minposition is made intouseful articles by shaping and formutes. Similar better states of curefor decachlorobutane ing the uncured composition. Thereafter, thearticle is 2 vulcanizates are shown by higher moduli: cured or crosslinked to permanent shape by the application of controlled amounts ofheat and pressure, temperatures of 120 to 195 degrees centigrade andpressures TABLE II of to 1000 pounds per square inch for two to ninetyCure minutes being useful. 40 w t S 20 M, t S The invention isillustrated by the following non-limitg a at 62 mg examples.Temperatures are expressed in degrees I C D C D centigrade and parts areby weight. All elastomeric formucmnpwton lations are ex ressed in termsof 0 art 0 er Tensile Stren th at Ultimate Elongation 1 d p 10 p S fpolym (poundslsqsareinch) 2,151 2,205 2,129 2,159 p y Modulus at 300%Elongation (pounds/ square inch) a..- 1,882 1,356 1,910 1,529 EXAMPLES,297 925 Elongation at Break, percent 322 507 345 419 Table Iillustrates and compares the invention with controls using other curingagents. In each case, the cured decachlorobutane composition shows aconsiderably Compositions E, F and G compare various chlorocarhigherdegree of cross linking, i.e., higher state of cure, bons in anelastomeric composition with substantially as evidenced by highermodulus, shorter elongation, better higher than normal loadings ofcarbon black. Compos1- low temperature properties and so forth. tion G,containing decachlorobutane, shows substantially TABLE I Composition A Bc D E F G H I .T K L Polyethylene 1 Ethylene-Propylene Rubber SRF CarbonBlacllri Ferric Oxide Deeaohlorobutane OotachloropropaneOotachlorocyclopentene Properties (press cure, 40 minutes at 160):

Tensile Strength at Ultimate Elongation (pounds/square inch) Modulus at200% Elongation. Modulus at 300% Elongation. Elongation at Break,percent- 1 Alathon, low density, E.I. du Pont de Nemours & Co. 2 EIR404, 43% ethylene by weight, ML- i, 0., appx. 42, Enjay Chemical Co. 320 Minutes at degrees centigrade.

Compositions A and B were tested for brittleness and lower loss intensile strength than Compositions E and F. flexural failure which arefunctions of cross link density 70 Composition K illustrates the use oflarger amount of and state of cure. Samples were subjected totemperatures decachlorobutane to achieve a yet higher state of cure of40 degrees centigrade. Composition A remained flexin a short timeperiod. ible, while Composition B was brittle and cracked whenAdditional compositions containing decachlorobutane flexed at thistemperature. Additional samples were suband various elastomers ormixtures of elastomers are jected to degree bends at room temperatureuntil 75 shown in Table III.

TABLE III Ethylene-Propylene Terpolymer 1 Ethylene-Propylene Copolymerm.Polyisobutylene Z Polybutadiene Styrene-Butadiene C HAF Carbon BlackProcess Oil Stearic Acid. Sulfur Zinc Oxide.

Ferric Oxide Zinc Carbonate- Tall Oil Decachlorobutane 2 2 2 2Properties:

Press Cured at 160 0., minutes 40 40 60 40 40 40 60 30 40 TensileStrength at Ultimate Elongation (pounds/square inch) 3, 240 3, 061 2,161 1, 311 1, 200 1,702 1, 207 1, 188 4, 086

Modulus at 300% Elongation 956 767 1, 000 1, 004 2, 442 Elongation atBreak, Percent 743 860 723 188 I 123 531 207 153' 484 1 N ordel 1070,Specific Gravity 0.85, E. I. du Pont de Nemours & Co.

1 Butyl 218, Appx. 2.5% Isoprene, ML-8, 100 degrees 71-80, EnjayChemical Co.

3 Ameripol CB-220, Cis'-1,4 p'olybutadiene, Goodrich Gulf Chemical Co.

4 Ameripol 1606 Cold Black Master Batch Oil and Carbon have beenseparated and shown separately. Goodrich Gulf Chemical Co. 5 Flexon 846Petroleum Process Oil, Humble Oil dz Refining Co.

High Aromatic Process Oil.

Substantially non-staining vulcanizates were obtained odors developedduring cure and retained afterwards and with decachlorobutane as thecuring agent. Constantly the danger of explosion. On the other hand,decachloronon-staining vulcanizates were obtained when compoundbutanevulcanizates have a high state of cure, which proing was carried out at105 degrees centigrade. No loss duces a superior product and eliminatesproblems asof curing agents by volatilization was observed when sociatedwith low state of cure. These problems include compounding was carriedout at the elevated temperature. mold stain, rough vulcanizate surface,poor mold release, On the other hand, octachlorocyclopentenevulcanizates poor properties at high filler loadings, low tensilestrength badly stained the chrome plated steel mold. The priorandbrittleness at low temperature. Thus, the decachloroart chlorocar-bonsalso badly stained molds made of steel butane curative of this inventionproduces superior vulor aluminum. canizates as compared to otherchlorocarbons, yet is free The vulcanizates containing decachlorobutanehad very of the drawbacks of the costly peroxide curatives. smooth shinysurfaces which are comparable to those 0b- Various changes andmodifications may be made in the tained when the vulcanizate contains aperoxide curamethod of this invention and in the composition ratios tivesuch as dicumyl peroxide. Vulcanizates containing of this invention.Certain preferred forms which have octachloropropane oroctachlorocyclopentene are less been described, and equivalents may besubstituted and shiny and have a rougher surface. not depart from thespirit and scope of this invention.

It was also surprising to note that vulcanizates contain- Thesemodifications are to be regarded as within the ing decachlorobutaneshowed substantially lower adhesion srope of this invention. to the moldand easier mold release than vulcanizates What is claimed is: containingoctachloropropane and/ or octachlorocyclopen- 1. A composition which canbe vulcanized comprising tene. This unusual property was demonstratedwhen the decachlorobutane in combination with sulfur and an variouscompositions were cured in a substantially flat elastomeric hydrocarbonpolymer.

2 /2 inch by 3 inch cavity mold, having a total surface 2. A compositionwhich can be Vulcanized comprising area of approximately 7.5 squareinches of which the from 0.1 to 30 parts of decachlorobutane incombination cavities for four dumbbell specimens take up one square withfrom 0.1 to 10 parts of sulfur and an elastomeric inch. Prior to loadingthe molds, the mold faces were composition containing 100 parts ofelastomeric hydrolightly coated with a silicone mold releasecomposition. carbon polymer.

The area of contact between the mold faces was 6.5 3. A compositionwhich can be vulcanized comprising square inches. A thin layer or flashof elastomeric comdecachlorobutane and a metallic accelerator incombipositions several mils thick remains in the area of connation withsulfur and an elastomeric hydrocarbon tact between the mold faces afterpressure is applied 5 polymer.

during vulcanization. After curing the compositions con- 4. Acomposition which can be vulcanized comprising tainingoctachlorocyclopentene and other chlorocarbons, decachlorobutane incombination with sulfur and a satuadhesion of this film to both moldfaces is strong making rated polymer derived from an alpha olefin.

separation of the mold faces difiicult. However, with dec- 5. Acomposition which can be vulcanized comprising aehlorobutanevulcanizates, separation of the mold faces decachlorobutane incombination with sulfur and ethylene is easy. propylene copolymer.

Decachlorobutane vulcanizates have a higher state of 6. A compositionwhich can be vulcanized comprising cure than those vulcanizates whichcontain chlorocarbons decachlorobutane in combination with sulfur andpolyof the prior art. Chlorocarbons such as octachloroproethylene. paneand octachlorocyclopentene yield vulcanizates hav- 7. A compositionwhich can be vulcanized comprising ing a low state of cure. Mold releaseof these vulcanizates decachlorobutane in combination with sulfur andethylene is relatively difiicult and there is a tendency of thevulpropylene ter-polymer. canizate to stick to the mold surface becauseof the 8. A composition which can be vulcanized comprising relativelyhigh adhesion of vulcanizate to the mold reladecachlorobutane incombination with sulfur and polytive to cohesive strength of thevulcanizate. Vulcanizates isobutylene. with decachlorobutane as thecuring agent are free from 9. A composition which can be vulcanizedcomprising certain of the disadvantages associated with peroxidedecachlorobutane in combination with sulfur and polyvulcanizates.butadiene.

The use of peroxide curatives for polymers is not 10. A process ofvulcanizing a polymerizate derived favored due to their comparative highcost, unpleasant from an alpha olefin which comprises heating the samein the presence of decachlorobutane and sulfur at a temperature and fora time sufficient to vulcanize the polymerizate. I v

11. A process of vulcanizing a polymerizate wherein the polymerizatecontains 100 parts of a polymer derived from an alpha olefin whichcomprises heating the same in the presence of from 0.1 to 30.0 parts ofdecachlorobutane and 0.1 to 10.0 parts of sulfur at a temperature fromabout 120 to about 195 degrees centigrade for 2 to 90 minutes.

12. A process of vulcanizing a polymerizate derived from an alpha olefinwhich comprises heating the same in the presence of decachlorobutane,sulfur and a metallic accelerator at a temperature and for a timesuificient to vulcanize the polymerizate.

13. A process of vulcanizing a polymerizate wherein the polymerizatecontains 100 parts of a polymer derived from an alpha olefin whichcomprises heating the same in the presence of from 0.1 to 30.0 parts of'dechlorobutane, 0.1 to 10.0 parts of sulfur, and from 0.1 to 10.0 partsof a metallic accelerator at a temperature from about 120 to 195 degreescentigrade for 2 to 90 minutes.

14. A reaction product of an elastomeric hydrocarbon polymer withdecachlorobutane and sulfur.

15. Arubbery heat reaction product of an elastomeric hydrocarbon polymerwith decachlorobutane, sulfur and a metallic accelerator resulting fromheating a mixture 8 of the polymer, decachlorob'utane, sulfur andmetallic accelerator.

16. A molded heat reaction product of an elastomer derived from an alphaolefin with decachlorobutane and 5 sulfur resulting from heating amixture of 100 parts of elastomer, from 0.1 to 30.0 parts ofdecachlorobutane and from 0.1 to 10.0 parts of sulfur at a temperatureand for a time sufficient to react the mixture.

17. A molded heat reaction product of an elastomer 10 derived from analpha olefin with decachlorobutane, sulfur and a metallic acceleratorresulting from heating a mixture of 100 parts of elastomer, from 0.1 to30.0 parts of decachlorobutane, from 0.1 to 10.0 parts of sulfur andfrom 0.1 to 10 parts of a metallic accelerator at a 15 temperature andfor a time sufiicient to react the mixture.

References Cited UNITED STATES PATENTS 5/1967 Wei et a1. 260-795 7/1967Wei et a1. 260-795 FOREIGN PATENTS 3/1955 Great Britain. 4/1963 Belgium.

5 JOSEPH L. SCHOFER, Primary Examiner.

D. K. DENENBERG, Assistant Examiner.

1. A COMPOSITION WHICH CAN BE CULVANIZED COMPRISING DECACHLOROBUTANE INCOMBINATION WITH SULFUR AND AN ELASTOMERIC HYDROCARBON POLYMER.